1. Field of the Invention
The present invention relates to the heating of liquids in a falling film heat exchanger, and more particularly to a screen arrangement for preventing solid particles in the liquid to be heated from plugging liquid distribution outlets of a perforated liquid distributing tray or reaching the heating surface of the heat exchanger.
2. Description of the Prior Art
Falling film plate type heat exchangers have a wide variety of industrial uses. Such falling film heat exchangers are shown and described in U.S. Pat. Nos. 3,332,469; 3,307,614 and 3,366,158. In such heat exchangers liquid to be heated by indirect heat exchange with vapor is directed to flow as a falling film down the external surfaces of two-plate heating elements to be heated by heat exchange with vapor circulating between the plates of those elements. One common arrangement for distributing the liquid so that the liquid flows evenly down the plate surfaces comprises a perforated horizontally disposed tray located above the tops of the plate heat exchange elements. Holes in the tray are arranged above the top edges of the plate elements.
The holes of such a perforated tray can become plugged or obstructed if the liquid to be heated carries large solid particles in suspension. For example, when a falling film type plate heat exchanger is used as an external heater for a batch digester in the wood pulping industry, wood particles entrained in the liquor can clog the holes of the heat exchanger's liquid distribution tray and thereby interfere with the even distribution of liquor to the plate elements.
The present invention provides a solution to the problem of the plugging of holes in liquid distribution trays and the like. Undesirable particles are diverted to bypass the tray and the heating surface.